High frequency receiving apparatus



. 5, 9 9- E. Y. ROBINSON 2,182,577

I HIGH FREQUENCY RECEIVING APPARATUS I Original Filed July 25, 1934 Inventor:

ErnestY. Robins n,

H is A torn e y.

Patented Dec. 5, 1939 UNITED STATES PATENT OFFICE,

Ernest Y. Robinson,

to General Electric Company,

New York Enficld, England, assignor a corporation of Original application July 25, 1934,- Serial No.

736,837. her 3, 1936, November 8, 1933 11 Claims.

means whereby the anode current in an electron discharge amplifier may be varied in a novel way with respect to the input voltage applied thereto.

In radio receivers employing automatic volume control circuits it has been found desirable to employ means for suppressing noise which occurs at times when the receiveris not in resonance with any received carrier wave. This has been accomplished by providing means to suppress all output from the receiver except when the input to the receiver exceeds a predetermined intensity. An object of my present invention is to provide an improved means for securing this result.

Still further objects of my invention relate to improved means for controlling the output of a radio receiver having automatic volume control means whereby the aural response of the receiver is controlled in such a way that it may be used as a sole guide in tuning the receiver.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Figs. 1 and 3 represent different embodimentsof my invention, and Fig. 2 represents cer tain characteristics of the operation of the form of the invention shown in Fig. 1.

5 Referring to Fig. 1 of the drawing I have shown therein a portion of the circuits of aradio receiver involving electron discharge devices I, 2 and 3. The electron discharge device 5 is a radio fre quency amplifier of the conventional variable mu type. this tube being provided with the well known variable pitch control grid 4, a screen 5,

and suppressor grid 5, the latter being connected directly to the cathode l. The control grid 4 is connected to a tuned input circuit 8 to which radio frequency electromotive forces may be sup- Divided and this application Septem- Serial No. 99,245. In Great Britain plied either from the antenna circuit, or preceding stages, not shown, of the receiver. The anode of the discharge device i is likewise connected to a tuned output circuit 9 which in turn is closely coupled to a tuned circuit ill comprising the input circuit of the electron discharge device 2. v

The discharge device 2, as shown, is one of the type having a cathode II which cooperates with an anode i2 in the manner of the electrodes of a diode. It also cooperates with a variable pitch control grid 4, screen grid l3, suppressor grid M and anode I5 in the same manner as in discharge device I. The anode of the dischargedevice 2 is connected to a tuned circuit H which is loosely coupled to a tuned circuit 18, these circuits being loosely coupled for high selectivity, the circuit it comprising the input circuit to the valve 3.

The electron discharge device 3 is provided with a cathode and two anodes l9 between the latter of which the tuned circuit i3 is connected, this portion of the discharge device 3 cooperating in the mannerof a full wave detector or rectifier. The discharge device 3 is also provided with five grids G1, G2, G3, G4, G5 and an anode which cooperate in a manner later to be described.

It will now be observed that high frequency oscillations supplied to the input circuit 8 are amplified in discharge device I and supplied through circuits 9 and of the discharge device 2, and also to grid t of device 2 in which they are amplified and supplied to circuit l1. Rectifier H, I2 is the automatic volumecontrol rectifier of the radio receiver, the

anode being connected to the cathode through a load resistance 2| and a cathode bias resistor 22, this latter resistor being connected between the cathode of the discharge device and the negative side of the power supply to the different discharge devices. This power supply is indicated by the conductors marked plus and minus and supplies of all of the discharge devices. It is bypassed for radio frequency currents by condenser C.

The current flowing between the cathode and anode l5 of discharge device 2 is sufficiently great to prevent any flow of current in the diode l l, 92 and in resistance 2| when the received carrier wave has an intensity less than a certain predetermined value. When the received high frequency electromotive force is greater than said predetermined intensity a unidirectional voltage appears upon resistance 2! causing the upper terminal thereof to become negative this negafrom v In to the diode rectifier energy to the different electrodes I tive unidirectional voltage being applied through the filter comprising resistance 23 and condenser 23, and input circuit 8, to the grid of discharge device E, and through input circuit H} to grid i of discharge device 2. In this way the grids of discharge devices i and 2 are driven negatively by an amount sufficient to maintain the signal wave electromotive forces in the circuit I'I substantially constant irrespective of any variations in intensity of the received carrier wave produced, for example, as by fading.

High frequency oscillations in the circuit i? are supplied to the rectifier section I8, 19 of the discharge device 3 whereby they are rectified. When this occurs a unidirectional voltage, and also the audio frequency voltage resulting from demodulation of the carrier wave, are produced upon resistance 24 which is connected between the cathode and an intermediate point on the inductance of the tuned circuit [8. The unidirectional voltage produced on this resistance is supplied to the control grid G1 of device 3 through a resistance 25. The audio frequency voltage is likewise applied to this grid through a condenser 26 which may be variably connected to the resistance 24 for manual volume control purposes. Grid G1 is a variable pitch grid similar to grids 4 and 4 of devices I and 2.

The action of discharge device 3 will now be described. It will be observed that the anode 29 of the discharge device 3 is connected to the positive side of the power source through a resistance 27 and that grids G2 and G4 are connected directly to the positive side of this supply source. These grids thus operate as electron receiving electrodes or anodes. The cat ode is connected to the negative side of the supply source through a resistance 28, and the grid G3 is connected through a resistance 29 to an intermediate point on a bleeder resistance 39 across the supply source.

In the absence of a signal in the circuit !8 having intensity greater than a predetermined amplitude, due to current flowing in resistance 28 and the tap connection of resistance 29 to resistance 30, the grid G3 is sufiiciently negative with respect to the cathode to preclude the flow of any current to anode 20. All of the current flowing through resistance 28 flows from the grid G2 to the cathode. This prevents any audio frequency output from appearingon resistance 21 where it might be tapped off through an output condenser 3| to any desired load circuit such as a loudspeaker or subsequent audio amplifier. This predetermined intensity may be so chosen as to preclude the production of noise currents in the output when the carrier is of less than a desired value.

As the signal electromotive force in circuits i! and It increases, however, the unidirectional voltage on resistance 2d increases thereby driving the grid G1 increasingly negative with respect to the cathode. This in turn reduces the amount of current flowing in resistance 28 and thereby causes the grid G3 to become gradually less negative with respect to the cathode. When the received signal exceeds the said predetermined amplitude current starts to flow in the resistance 2'! across which the audio voltage appears which is supplied through the condenser 3| to the load circuit. This output thus increases in accordance with the intensity of the received signal wave due to the increased amplification of the amplifier section of the valve 3 in response to the increased carrier wave.

In this way noise suppression in the receiver is effected. Electromotive forces supplied to the grid G1, due to atmospheric electricity, static, etc., are not ordinarily of sufficient mean value to affect appreciably the voltage on grid G3. By means of resistance 29 and by-pass condenser 29', the circuit of grid G3 is given a time constant such that large atmospheric and static electromotive forces do not appreciably affect this grid. In this way and by proper adjustment of the tap point of resistance 29 to resistance 30 atmosphere and other interference may be completely suppressed.

The tuning elements of the tuned circuits 8, 9, if), H and i8 may if desired be provided with unicontrol means whereby the receiver may be tuned to any desired frequency. Preferably, however, these circuits are comprised in the intermediate frequency portion of a superheterodyne receiver whereby they may be tuned to a single fixed frequency. In such a receiver the intermediate frequency is supplied to the circuit 8 from the first detector, not shown, which may be tuned by unicontroi with the tuning of a local oscillator and antenna circuit, which may include radio amplifiers. These portions of the equipment being entirely conventional are omitted for simplicity of the drawing. Thus when the receiver is in tune with any desired carrier wave a constant intermediate frequency is supplied to the circuit 8. Upon variation of the unicontrol member in either direction from the resonance position, however, the intermediate frequency varies and is, therefore, rapidly attenuated by reason of the selectivity of the radio, and intermediate frequency, circuits.

The operation of the system with respect to aural tuning may now be described. Let us assume that tuned circuits 8, 9, I 0, I! and [8 are all adjusted for resonance with a desired intermediate frequeney, which varies in amplitude, as due to fading. Due to the automatic volume control action of diodes H and I2 the amplification of amplifiers l and 2, and if desired, earlier radio frequency stages, is varied inversely with the intensity of the received carrier wave with the result that a substantially constant carrier electromotive force is maintained in circuits H and Hi. This result may be obtained to an extremely high degree particularly in view of the fact that the automatic volume control results from rectification of the high frequency voltage at a point in the circuit prior to the amplification produced by the amplifier section of discharge device 2.

The amplification of discharge device 3, therefore, remains constant irrespective of the intensity of received signals, and the output audio volume likewise remains constant.

Let us assume now that the input voltage applied to the receiver is constant but that the intermediate frequency varies by reason of variation of the tuning of the local oscillator from the point where the exact desired intermediate frequenoy is produced. As this variation in frequency occurs the signal intensity applied to the rectifier ll, i2, of course, reduces by reason of the selectivity of the circuits thereby causing increased amplification of the discharge devices I and 2 and a tendency to cause either a constant or an increased carrier voltage in the circuit I! over a certain range of operation of the tuning control. However, owing to the greater selectivity of the circuits between the input to the receiver and the anodes 49, over that between the input to the receiver and the anode II. a reduction in the signal voltage appearing in circuit l8 immediately occurs, this reduction in carrier wave voltage greatly reducing the amplification of the discharge device 3 until a point is reached where no output occurs. It will thus be seen that in the tuning operation a relatively sharp maximum in the audio outputof the receiver is produced when the receiver is exactly in tune with the received carrier wave. This characteristic of the apparatus greatly facilitates the tuning of the radio receiver by the aid of the aural response notwithstanding the use of the automatic volume control circuits.

This latter characteristic of the apparatus also has the desired advantage that it reduces the unpleasant sounds produced in the radio receiver commonly known as side band shriek. These sounds are produced when the radio receiver is adjusted for resonance with a side band of a received carrier wave owing to the increased amplification of the amplifiers as the receiver is cletuned for resonance with the carrier wave. Since in accordance with my invention the amplification of the discharge device 3 is reduced at this time these side band shrieks are removed.

To increase the effectiveness of the operation of my apparatus both for aural tuning purposes and for reduction of side band shriek, and interchannel gain, it is desirable that the selectivity of the portion of radio receiver prior to the anodes is be as much greater than that of the portion of the receiver prior to anode l2 as possible. For this reason circuits 9 and H] desirably are relatively closely coupled whereas circuits H and I8 are relatively loosely coupled. Of course this difference in selectivity may be increased by any of the well known expedients, such as the inclusion of additional stages of amplification or tuning between the circuits and I9.

It will thus be seen that discharge device 3 operates as an audio amplifier, the amplification being controlled by the voltage on resistance 24. It also operates as a direct current amplifier of the unidirectional voltage on resistance 24, the voltage. after amplification, being applied to grid G3 with polarity opposite to that applied to grid G1 by resistance 24.

In Fig. 2 I have shown certain characteristics of the operation of the discharge device 3 of Fig. 1. The curves a, b, c, d, and e of this figure express the relation between voltage applied to the control grid plotted as abscissa and current Ia flowing in the anode of the discharge device for different values of voltage between the cathode and the grid G3. The curve a expresses the relation between the current in the anode and the control grid voltage when the voltage between the grid G3 and the cathode is relatively large, whereas the curve e expresses the same relation when the voltage between the cathode and the voltage G3 is relatively small, curves b, c, and d expressing the same relation for intermediate values of the voltage between the cathode and the rid Ge.

In the circuit illustrated the variation of the unidirectional voltage applied to control grid G1 causes a variation in the unidirectional voltage EGG appearing between the cathode and the grid Ga. The dotted line represents the locus of the latter voltage occurring as the control grid voltage increases. That is, the curve is drawn through points on the curves a to e, each of which points corresponds to the value of Iawhich may occur when the voltage is such as to produce a voltage corresponding to the different curves. of course the pitch of this curve may be varied by variation of the different resistances and connections affecting the potentials on grids E and amplifiers such as amplifier I. The diode 31 opcrates for aural tuning control and is supplied with high frequency currents from circuit 9 through additional tuned circuits 45, 46 and 38. The diode 39 in cooperation with the discharge device 3 operates to effect noise suppression.

It will be observed that the cathode of the discharge device 3 is connected to the negative side of the supply source not only through the bias resistor 28 but also through a dropping resistance 4!). The negative end of the dropping resistance is connected to the grid G3 through a resistance M, connected across the diode 39, and a filter comprising resistance 42 and condenser 43. The cathode of the diode 39 is'connected through coupling condenser 44 to one side of the aural tuning circuit 38 whereby this discharge device is effectively energized with high frequency oscillations. The grid G3 in the absence of a signal of greater than a predetermined intensity is sufliciently negative with respect to the cathode to prevent the flowof anode current and thus audio output is precluded from this device. Resistance 4| is so poled, however, that when signals of greater than a predetermined intensity are received the negative voltage of the grid G3 is reduced to such an extent that current starts to flow in the anode of the discharge device. The voltage appearing on resistance 4|, however, is sufficiently great to cause the tube 3 to produce a switch-like action whereby the output signal when sufficiently re: duced from normal suddenly drops to zero. In this way noise suppression during periods when the receiver is off tune with any carrier wave or when the received signals are of less than a predetermined intensity is effective.

Grid G1 is biased negatively from the automatic volume control conductor 33 through load resistance 34 of diode 31 and filter resistor 35. Resist,- ance 34 is so poled as to reduce the negative voltage applied to the grid G1 in accordance with the intensity of oscillations supplied through cirto increase the fiow of current to the anode. In.

this way a distinct maximum of aural response for the receiver is obtained when the tuning control is varied through resonance and thus the receiver may be tuned solely by guidance of-the aural response.

In other respects the operation of the equipment of Fig. 3 will be readily understood from the explanation already given it being noted further only that the additional tuned circuits and 46 are interposed between circuit 9 and circuit 38 to increase the difference in selectivity between the portion of the receiver prior to the automatic volume control diode H l2 and that portion prior to the aural tuning control diode 3'1. These circuits are connected together across the power supply mains by capacity 47 and may, of course, be employed in connection with the equipment of Fig. 1 if increased selectivity between circuits 9 and 38 be desired.

While I have shown particular embodiments of my invention it will of course be understood that I do not Wish to be limited thereto since many modifications both in the circuit arrangement and in the instrumentalities employed may be made, and that I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Let'ers Patent of the United States is:

1. In combination, an electron discharge device having an anode, a cathode, and a grid interposed between said anode and cathode, means to supply to said grid a voltage varying negatively with respect to said cathode, and means responsive to variations of said voltage in the nega tive direction from the cathode voltage to increase the fiow of electrons to said anode.

2. In combination, an electron discharge device having an anode, a cathode, and a grid interposed between said anode and cathode, means to supply a negative voltage to said grid, and means to increase the magnitude of current in said anode in response to increase in the negative volton said grid.

In combination, an electron discharge amplifier having an anode, a cathode, and a plurality of control electrodes interposed between said anode and cathode, means to supply to said amplifi r currents to be amplified, means to supply to one of said electrodes a unidirectional voltage to control the amplification of said amplifier, means utilizing another of said electrodes to amplify unidirectional electromotive force, and race ns to supply the amplified electromotive force to a third of said electrodes to control the current in said anode, and a load circuit between said anode and cathode for currents representing said cu rents to be amplified.

l. In combination, an electron discharge device having an anode, a cathode and an intermediate electron receiving electrode, means to supply positive potential with respect to said cathode to said anode and intermediate electrode, a control electrode on each side of said intermediate electrode, means to supply a control voltage to one of said control electrodes, and means utilizing intermediate electrode to amplify said control voltage and supply it to the other of said con-' trol electrodes.

5. Ihe combination, in a radio receiver, of an electron discharge device having an anode, a cathode, and a plurality of electrodes interposed therebetween including an inner positive electrode and two outer electrodes arranged on opposite sides of said inner electrode, and means responsive to a signal to supply voltages to said outer electrodes varying in opposite senses thereby to control the proportion of electrons which fiow from said cathode to said inner electrode and anode respectively.

6. The combination, in a radio receiver, of an electron discharge device having an anode, a cathode, and a plurality of electrodes interposed therebetween including an inner positive electrode and two outer electrodes arranged on opposite sides of said inner electrode, means responsive to a signal to supply a negative voltage to said outer electrode nearer the cathode, means responsive to said voltage to supply a voltage to the outer electrode nearer the anode varying in opposite sense to that on said other electrode nearer the cathode thereby to increase the current flowing to said anode.

7. In combination, an electron discharge device having a cathode, a control electrode, an anode, a second control electrode and a second anode all located in the electron stream from said cathode in the order named, means to supply to said first control electrode currents to be amplified and an electromotive force to control the amount of said amplification, means utilizing said first anode to amplify said control electromotive force and to supply said amplified electromotive force to said second control electrode thereby to control the flow of electrons to said second anode, and a load circuit for said currents to be amplified connected between said cathode and second anode.

8. The combination, in a radio receiver, of an electron discharge device having a cathode, an anode and at least three electrodes spaced at different distances from said cathode and between said cathode and anode, means to supply to the intermediate of said electrodes a positive potential and to that one of said electrodes nearest the anode a negative potential of such value that substantially no current flows in said anode, means to supply received signals to be amplified to that one of said electrodes nearest the oathode, and means operative to reduce the voltage 9. The combination, in a radio receiver, of an electron discharge device having a cathode, an anode, and at least three electrodes spaced at diiTerent distances from said cathode and between said cathode and anode, means to supply to the intermediate of said electrodes a positive potential and to that one of said electrodes nearest the anode a negative potential of such value that substantially no current flows in said anode, means to supply received signals to be amplified and negative unidirectional voltage having amplitude varying in accordance with the intensity of said signals to that one of said electrodes nearest the cathode, means responsive to said unidirectional voltage to reduce the voltage on said electrode nearest the anode to such an extent that said signal currents appear on said anode when their intensity exceeds a predetermined value.

10. The combination, in a variably tuned radio receiver, of an electron discharge device having an anode, a cathode, and at least two grids interposed between said anode and cathode, and an additional electrode between said two grids, means normally to supply to said additional electrode and anode positive voltages and to said grids negative voltage, said negative voltages being of such value that electrons flow to said additional electrode but not to said anode, means to supply signal voltage to be amplified to the grid nearer the cathode, and means to reduce said negative voltages in accordance with the intensity of the received signals as affected by variation of the tuning of said receiver, said negative voltages being so controlled that signal current flows in said anode only when the received signals exceed a predetermined value and then vary with variation of said tuning to such an extent as to produce a marked aural maximum ,from said output device when said receiver is in exact resonance with a received signal.

vice having a cathode, a control electrode, and an output electrode, an output circuit connected between said output electrode and cathode, and a control circuit connected between said control electrode and cathode, said control electrode being positioned between said cathode and output electrode within said discharge device, and means to increase the magnitude of current in said output circuit in response to variations in voltage on said control electrode in the negative direction from the voltage of said cathode.

ERNEST Y. ROBINSON.

11. In combination, an electron discharge de- 

